The possibility of using magnetic elements for computation has been of recent interest. Computers using magnetic processors would have the potential for low power requirements, and indefinite data retention during power interruptions. Some Magnetoresistive Random Access Memory (MRAM)-based reconfigurable logic elements have been developed. For example, Ney et al., Nature, 425(6957): 485-487, 2003 reported MRAM-based devices where a tunneling current travels through a barrier layer between a high coercivity (hard) layer and a low coercivity (soft) layer. In Ney's system, signal contrast results from the relative alignment of the magnetization (parallel or antiparallel) in the hard and soft layers. Reconfiguration of the gate is possible using strip lines. However, in all of these MRAM systems, good signal contrast relies on the formation of thin tunnel barriers, which are susceptible to chemical degradation, defect formation and electromagnetic pulse (EMP) damage. In other work, magnetic systems using either domain wall motion or flipping of dipole states have been used to process binary data.
A vortex magnetization state that closes on itself, most often in a ring-shaped structure, exhibits excellent stability once the magnetization is written into the material. The closed loop structure has very symmetric fields and thus, does not affect nearby elements significantly. Multiple elements may therefore be arranged in close proximity to one another with an ultimate area density approximated at 400 Gbits/in2. However, the low leakage fields of these elements can make it difficult or impossible to detect the direction of the vortices (i.e., the stored bits of “1” and “0”) using conventional magneto-optical readout methods.
Readout from planar magnetic devices is typically accomplished using either a polarized Magneto-Optic Kerr Effect (MOKE) signal from the entire device or Magnetic Force Microscopy signals from local regions. MOKE is a non-contact optical technique that uses either a polar, longitudinal or transverse light beam. A small portion of the incident light beam undergoes a polarization rotation upon reflection, and this polarization rotation is proportional to magnetization and off-diagonal elements of the sample's dielectric matrix. The polar Kerr effect has been used in magneto-optic storage applications, but for the examination of in-plane magnetization, the longitudinal or transverse Kerr effect must be used, despite the inherently small signal associated with each of these geometries.